The invention relates to a detector for detection of ionizing radiation to an apparatus for use in planar beam radiography and to a method for detecting ionizing radiation.
A detector and an apparatus of the kind mentioned above are described in the copending U.S. application Ser. No. 08/969,554 and in the copending SE applications SE 9901327-8, SE 9901324-5, SE 9901325-2 and SE 9901562-0, which are incorporated herein by reference. Another detector and apparatus of the kind mentioned above is disclosed in EP-A1-0 810 631.
Gaseous detectors are a viable alternative to solid state detectors at photon energies  less than 10 keV. The main advantages with gaseous detectors are that they are cheap to manufacture compared to solid state detectors, and they can employ gas multiplication to strongly (several orders of magnitude) amplify the signal amplitudes. However, at energies  greater than 10 keV the gaseous detectors are less attractive because the stopping power of the gas decreases rapidly with increased photon energy. This results in a spoiled position resolution due to extended tracks of electrons (long-range electons), which are created as a result of the X-ray absorption.
The present invention is directed to a detector for detection of ionizing radiation, which can employ avalanche amplification, and provides improved position resolution, and can operate in a wider energy range of incoming radiation than prior art detectors.
This and other objects are attained by a detector for detection of ionizing radiation, comprising a chamber filled with an ionizable gas, first and second electrode arrangements, provided in said chamber with a space between them, said space including a conversion and drift volume, an electron avalanche amplification unit arranged in the chamber, and wherein said electron avalanche amplification unit includes at least one avalanche cathode and at least one avalanche anode between which a voltage is to be applied for creation of at least one electric field for avalanche amplification, and the distance between the first and second electrode arrangements being smaller than an attenuation length of fluorescent photons present in the at least one electric field for avalanche amplification.
The above detector can further be given a length, in the direction of the incoming radiation, for achieving a desired stopping power, which makes it possible to detect a major portion of the incoming radiation.
In the above detector electrons that are released by interactions between photons and gas atoms can be extracted in a direction essentially perpendicular to the incident radiation to obtain a very high position resolution.
The above detector, which can also operate at high X-ray fluxes without performance degradation, has a long lifetime.
The above detector can also effectively detect any kind of radiation, including electromagnetic radiation as well as incident particles, including elementary particles.
The above detector is also simple and cheap to manufacture.
The present invention is also directed to an apparatus for use in planar beam radiography, comprising at least one one-dimensional detector for detection of ionizing radiation, which can employ avalanche amplification, and provides improved position resolution, and can operate in a wider energy range of incoming radiation than prior art detectors, and which can be manufactured in a simple and cost effective way.
This and other objects are attained by an apparatus for use in planar beam radiography, comprising an X-ray source, a substantially planar beam unit for forming a substantially planar X-ray beam positioned between said X-ray source and an object to be imaged, and the distance between the first and second electrode arrangements being smaller than a length of electron tracks of long-range electrons released from gas atoms present in the at least one electric field for avalanche amplification and/or ions as a result of interaction with X-ray photons.The above apparatus can be used in planar beam radiography, e.g. slit or scan radiography, where an object to be imaged only needs to be irradiated with a low dose of X-ray photons, while an image of high quality is obtained.
The above apparatus can also be used in planar beam radiography, in which a major fraction of the X-ray photons incident on the detector can be detected, for further counting or integration in order to obtain a value for each pixel of the image.
The above apparatus can also be used in planar beam radiography, in which image noise caused by radiation scattered in an object to be examined is strongly reduced.
The above apparatus can also be used in planar beam radiography, in which image noise caused by the spread of X-ray energy spectrum is reduced.
The above apparatus can also be used in planar beam radiography, including a detector which can operate at high X-ray fluxes without a performance degradation and has a long lifetime.
The present invention is also directed to a method for detection of ionizing radiation, which employs avalanche amplification, provides improved position resolution, and is efficient in a wider energy range of incoming radiation than prior art methods, and which can be implemented in a simple and cost effective way.
This and other objects are attained by a method for detecting ionizing radiation, comprising the steps of permitting the radiation to interact with gas atoms in a gas filled conversion and drift volume, to create released electrons, subjecting the electrons to an electric field in the conversion and drift volume, the electric field being substantially perpendicular to the direction of the radiation, causing electron avalanches by using the electric field to force the electrons to enter one of a plurality of regions, each with a concentrated electric field, detecting the electron avalanches using read-out elements, and discriminating fluorescent photons emitted in said radiation step.
In the above method, it possible to detect a major portion of the incoming radiation.
In the above method, electrons released by interactions between photons and gas atoms are extracted in a direction perpendicular to the incident radiation to obtain a very high position resolution.
The above method can also be used at high X-ray fluxes.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However; it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.